Article IV, Section 19, Constitution of the Commonwealth of Virginia:
"Slaves hereafter emancipated shall forfeit their freedom by remaining in the Commonwealth more than twelve months after they become actually free, and it shall be the duty of the General Assembly to prescribe proper regulations for reducing such negroes to slavery."
Where are the exemptions?
...did not affect free blacks already living there...
But could have. Article IV, Section 20, Constitution of the Commonwealth of Virginia:
"The General Assembly may profit the future emancipation of slaves, impose such restrictions and conditions as they shall deem proper on the power of slave owners to emancipate their slaves; and may pass laws for the relief of the Commonwealth from the free negro population, by removal or otherwise."
It illustrates something I've opined in the past, that white Americans 100 years ago simply didn't see blacks as being part of society. Here, Virginia's legislature is talking about them like a rat problem.